<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <!-- 移动端特有设置，解决移动端屏幕过小，放不下正常网页的问题 -->
    <!-- <meta name="viewport" content="width=device-width"> -->
    <!-- 当不设置viewport时，视口大小默认为980 -->
    <!-- 可通过js动态设置viewport -->
    <script>
       (function () {
      var metaEl = document.createElement('meta');
      var scale = devicePixelRatio;
      metaEl.setAttribute('name', 'viewport');
      metaEl.setAttribute('content', 'initial-scale=' + (1/scale) + ', maximum-scale=' + (1/scale) + ', minimum-scale=' + (1/scale) + ', user-scalable=no');
      document.documentElement.firstElementChild.appendChild(metaEl);
        })();
    </script>
    <title>Document</title>
    <style>
        #box{
            width: 200px;
            height:200px;
            background-color: red;
        }
    </style>

    <script>
        console.log("像素比：",window.devicePixelRatio)
        // 像素比：原先1px的内容放大到到devicePixelRatio px显示
    </script>
</head>
<body>
    <div id="box">hello 移动端</div>
</body>
</html>